Semiconductor device having metal gate and manufacturing method thereof

ABSTRACT

A method of manufacturing a semiconductor device having metal gate includes providing a substrate having a first transistor and a second transistor formed thereon, the first transistor having a first gate trench formed therein, forming a first work function metal layer in the first gate trench, forming a sacrificial masking layer in the first gate trench, removing a portion of the sacrificial masking layer to expose a portion of the first work function metal layer, removing the exposed first function metal layer to form a U-shaped work function metal layer in the first gate trench, and removing the sacrificial masking layer. The first transistor includes a first conductivity type and the second transistor includes a second conductivity type. The first conductivity type and the second conductivity type are complementary.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 13/158,479filed on Jun. 13, 2011, and incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a semiconductor device having a metal gate andmanufacturing method thereof, and more particularly, to a semiconductordevice having a metal gate and manufacturing method applied with a gatelast process.

2. Description of the Prior Art

With a trend toward scaling down the size of the semiconductor device,work function metals are used to replace the conventional polysilicongate to be the control electrode that competent to the high-K gatedielectric layer. The conventional dual metal gate methods arecategorized into gate first process and gate last process. Among the twomain processes, the gate last process is able to avoid processes of highthermal budget and to provide wider material choices for the high-K gatedielectric layer and the metal gate, and thus gradually replaces thegate first process.

Please refer to FIG. 1, which is a schematic drawing illustrating aconventional semiconductor device having a metal gate fabricated by thegate last process. In the conventional gate last process, a dummy gateor a replacement gate is formed on a substrate 100 and followed by stepsof forming a conventional metal-oxide semiconductor (MOS) transistordevice 110 and forming an inter-layer dielectric (ILD) layer 120.Subsequently, the dummy/replacement gate is removed to form a gatetrench. Then the gate trench is filled with work function metalsrequired by different conductivity type. However, layer 130 such asbarrier layer or strained stress layer is often formed in the gatetrench before forming the metals. And each layer 130 reduces an openingwidth of the gate trench by forming overhangs as depicted by circle A inFIG. 1. The overhang problem makes it difficult to fill the gate trenchwith the work function metal layer 140. Serious overhang problem such asoverhang merging or the metals layer 140 merging even results in a seam160 in the gate trench and makes the filling metal layer 150 cannot beformed in the gate trench as desired. Eventually, the electricalperformance of the transistor device 110 having the metal gate isdeteriorated.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda method of manufacturing a semiconductor device having metal gate. Themethod includes providing a substrate having a first transistor and asecond transistor formed thereon, the first transistor having a firstgate trench; forming a first work function metal layer in the first gatetrench; forming a sacrificial masking layer in the first gate trench;removing a portion of the sacrificial masking layer to expose a portionof the first work function metal layer; removing the exposed first workfunction metal layer to form a U-shaped work function metal layer; andremoving the sacrificial masking layer. The first transistor furtherincludes a first conductivity type and the second transistor furtherincludes a second conductivity type, and the first conductivity type andthe second conductivity type are complementary.

According to a second aspect of the present invention, there is provideda method of manufacturing a semiconductor device having metal gate. Themethod includes providing a substrate having a first transistor and asecond transistor formed thereon, the first transistor having a firstgate trench formed therein, the second transistor having a second gatetrench formed therein, and an opening width of the second gate trench islarger than an opening width of the first gate trench; forming a firstwork function metal layer in the first gate trench; forming asacrificial masking layer in the first gate trench and the second gatetrench; forming a patterned photoresist covering the second transistorand exposing the sacrificial masking layer in the first gate trench onthe substrate; removing a portion of the sacrificial masking layer toexpose a portion of the first work function metal layer; and removingthe exposed first work function metal layer to form a U-shaped workfunction metal layer in the first gate trench.

According to a third aspect of the present invention, there is provideda semiconductor device having a metal gate. The semiconductor deviceincludes a substrate having a first gate trench and second gate trenchformed thereon, a gate dielectric layer respectively formed in the firstgate trench and the second gate trench, a first work function metallayer formed on the gate dielectric layer in the first gate trench, asecond work function metal layer respectively formed in the first gatetrench and the second gate trench, and a filling metal layer formed onthe first work function metal layer and the second work function metallayer. The second work function metal layer formed in the first gatetrench includes an inverted Ω shape.

According to the method of manufacturing a semiconductor device havingmetal gate provided by the present invention, the sacrificial maskinglayer not filling the first gate trench is formed to protect a portionof the first work function metal layer in the first gate trench.Therefore the unnecessary first work function metal layer on thesubstrate and the overhang at the opening of the first gate trench areremoved. Consequently, layers such as the second work function metallayer and the filling metal layer are successfully formed in the firstgate trench without any seam. Therefore the semiconductor device havingmetal gate provided by the present invention has the advantage ofimproved reliability.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing illustrating a conventional semiconductordevice having a metal gate fabricated by the gate last process.

FIGS. 2A-8 are schematic drawings illustrating a method of manufacturinga semiconductor device having metal gate provided by a first preferredembodiment of the present invention; wherein

FIG. 2A is a drawing illustrating the method provided by the firstpreferred embodiment;

FIG. 2B is a drawing illustrating a modification to the first preferredembodiment; and

FIGS. 3-8 are schematic drawings illustrating steps subsequent to FIG.2A.

FIGS. 9-12 are schematic drawings illustrating a method of manufacturinga semiconductor device having metal gate provided by a second preferredembodiment of the present invention.

FIGS. 13-17, which are schematic drawings illustrating a method ofmanufacturing a semiconductor device having metal gate provided by athird preferred embodiment of the present invention.

FIG. 18 is a drawing illustrating a modification to the third preferredembodiment.

DETAILED DESCRIPTION

Please refer to FIGS. 2A-8, which are schematic drawings illustrating amethod of manufacturing a semiconductor device having metal gateprovided by a first preferred embodiment of the present invention. Asshown in FIG. 2A, the preferred embodiment first provides a substrate200 such as a silicon substrate, a silicon-containing substrate, or asilicon-on-insulator (SOI) substrate. A plurality of shallow trenchisolation (STI) 202 is formed in the substrate 200 for providingelectrical isolation. A first transistor 210, a second transistor 212,and a third transistor 214 are formed on the substrate 200. The firsttransistor 210 and the third transistor 214 include a first conductivitytype, the second transistor 212 includes a second conductivity type, andthe first conductivity type and the second conductivity type arecomplementary. The first transistor 210 and the second transistor 212having the complementary conductivity types are electrically isolatedfrom each other by the STI 202. Although the first transistor 210 andthe third transistor 214 include the same conductivity type, the firsttransistor 210 and the third transistor 214 include different linewidths. For example, the first transistor 210 is the transistor devicewith line width smaller than 40 nanometer (nm) such as the logic circuitdevice while the third transistor 214 is the transistor device with linewidth larger than 0.15 micrometer (μm) such as the static random accessmemory (SRAM) device. In the preferred embodiment, the firstconductivity type is the p-type and the second conductivity type is then-type. However, those skilled in the art would easily realize that itis not limited to have the first conductivity type being the n-type andthe second conductivity type is the p-type.

Please refer to FIG. 2A. The first transistor 210, the second transistor212, and the third transistor 214 respectively include a gate dielectriclayer 204 and a dummy gate layer 206 such as a polysilicon layer. Thegate dielectric layer 204 can be a conventional silicon oxide (SiO)layer or a high-K gate dielectric layer. The first transistor 210, thesecond transistor 212, and the third transistor 214 respectively includea first light doped drain (LDD) 220, a second LDD 222 and a third LDD224, a spacer 226, and a first source/drain 230, a second source/drain232 and a third source/drain 234. Salicides 236 are formed on the firstsource/drain 230, the second source/drain 232 and the third source/drain234. After forming the first transistor 210, the second transistor 212and the third transistor 214, a contact etch stop layer (CESL) 240 andan inter-layer dielectric (ILD) layer 242 are sequentially formed on thesubstrate 200. Additionally, selective epitaxial growth (SEG) method canbe utilized to form the sources/drains 230/232/234 in the preferredembodiment. Since the steps and material choices for the abovementionedelements are well-known to those skilled in the art, those details areomitted herein in the interest of brevity.

Please still refer to FIG. 2A. After forming the CESL 240 and the ILDlayer 242, a planarization process is performed to remove a portion ofthe CESL 240 and the ILD layer 242 to expose the dummy gates 206 of thefirst transistor 210, the second transistor 212 and the third transistor214. Thereafter, a patterned hard mask 250 is formed on the substrate200. The patterned hard mask 250 preferably is a multi layer formed tocover the second transistor 212. After forming the patterned hard mask250, a proper etching process is performed to remove the dummy gates ofthe first transistor 210 and the third transistor 214 to respectivelyform a first gate trench 260 in the first transistor 210 and a thirdgate trench 264 in the third transistor 214. During forming the firstgate trench 260 and the third gate trench 264, the patterned hard mask250 renders protection to the second transistor 212. Because the openingwidth of the gate trench is equal to the line width of the dummy gate206, an opening width of the third gate trench 264 is larger than anopening width of the first gate trench 260 as shown in FIG. 2A. Afterthe etching process, the gate dielectric layer 204 is exposed in bottomsof the first gate trench 260 and the third gate trench 264. It isnoteworthy that a high-K first process can be integrated into the methodprovided by the preferred embodiment. Accordingly, the gate dielectriclayer 204 includes a high-K gate dielectric layer, and the high-k gatedielectric layer is selected from the group consisting of siliconnitride (SiN), silicon oxynitride (SiON) and metal oxide. And the metaloxide comprises hafnium oxide (HfO₂), hafnium silicon oxide (HfSiO₄),hafnium silicon oxynitride (HfSiON), aluminum oxide (Al₂O₃), lanthanumoxide (La₂O₃), lanthanum aluminum oxide (LaAlO), tantalum oxide (Ta₂O₅),zirconium oxide (ZrO₂), zirconium silicon oxide (ZrSiO₄), or hafniumzirconium oxide (HfZrO₄).

According to a modification to the preferred embodiment, a patternedphotoresist (not shown) is formed on the substrate 200 after exposingthe dummy gate 206 of the first transistor 210, the second transistor212, and the third transistor 214 by the planarization. The patternedphotoresist covers the second transistor 212 and exposes the firsttransistor 210 and the third transistor 214. During removing the dummygate 206 of the first transistor 210 and the third transistor 214, thepatterned photoresist severs as an etching mask for protecting the dummygate 206 of the second transistor 212.

Please refer to FIG. 2B, which is a drawing illustrating anothermodification to the first preferred embodiment. As shown in FIG. 2B, ahigh-K last process can be integrated into the preferred embodiment. Inthis approach, the gate dielectric layer 204 is a conventional SiO layerand is removed from the first gate trench 260 and the third gate trench264 after forming the first gate trench 260 and the third gate trench264. Then, a high-K gate dielectric layer 204 a including materials asmentioned above is formed in the first gate trench 260 and the thirdgate trench 264. As shown in FIG. 2B, the high-K gate dielectric layer204 a formed in the first gate trench 260 and the third gate trench 264includes an U shape and covers sidewalls and bottoms of the first gatetrench 260 and the third gate trench 264.

Additionally, as shown in FIG. 2A, after forming the first gate trench260 and the third gate trench 264, or after forming the high-K gatedielectric layer 204 a, an inter layer 208 is selectively formed in thefirst gate trench 260 and the third gate trench 264 if required. Theinter layer 208 includes a barrier layer, a strained stress layer, atuning metal layer, or the combination thereof, but not limited to this.

Please refer to FIG. 2A again. Then, a first work function metal layer270 is formed in the first gate trench 260 and the third gate trench264. It is noteworthy that an overhang as depicted in Circle 272 isalways formed at the openings of the first gate trench 260 when formingthe first work function metal layer 270. It is conspicuous that theopening width of the first gate trench 260 is smaller; therefore theoverhang 272 generates more serious impact to the opening width of thefirst gate trench 260. As shown in FIG. 2A, the overhang 272 of firstwork function metal layer 270 reduces the opening width of the firstgate trench 260. The first work function metal layer 270 serves as workfunction metal for p-type transistor and includes titanium nitride(TiN), titanium carbide (TiC), tantalum nitride (TaN), tantalum carbide(TaC), tungsten carbide (WC), or aluminum titanium nitride (TiAlN).However, those skilled in the art would easily realize that the firstwork function metal layer 270 is not limited to the abovementionedmetals, it can include materials having a work function between about4.8 eV and about 5.2 eV. And the first work function metal layer 270 canbe a single-layered or multi-layered structure.

Please refer to FIG. 3. After forming the first work function metallayer 270, a sacrificial masking layer 280 is formed on the substrate200. The sacrificial masking layer 280 is a layer have superiorgap-filling characteristic such as a bottom anti-reflective coating(BARC) layer, a polysilicon layer, a Si-rich layer with silicon danglingbond (SHB) lower than 43%, a spin-on glass (SOG) layer, a sacrificiallight absorbing material (SLAM) layer, or an oxide-rich layer such asDUO™ (manufacturing by Honeywell Electronic Materials), but not limitedto this. Though the sacrificial masking layer 280 is a single-layeredstructure as shown in FIG. 3, the sacrificial masking layer 280 can be amulti-layered structure. As shown in FIG. 3, the sacrificial maskinglayer 280 is also formed in the first gate trench 260 and the third gatetrench 264. After forming the sacrificial masking layer 280, a patternedphotoresist 282 is formed on the substrate 200. The patternedphotoresist 282 covers at least the third transistor 214 but exposes thefirst transistor 210 and the second transistor 212.

Please refer to FIG. 4. Next, an etching back process is performed toremove a portion of the sacrificial masking layer 280 in the first gatetrench 260 and on the substrate 200 with a proper etchant such as CO orO₂ plasma. After the etching back process, a surface of the sacrificialmasking layer 280 is lower than the opening of the first gate trench260, that is, lower than a surface of the ILD layer 242. Thus, a portionof the first work function metal layer 270 on the substrate 200 and inthe first gate trench 260 is exposed. During the etching back process,the sacrificial masking layer 280 in the third gate trench 264 isprotected by the patterned photoresist 282, therefore it remainsimpervious to the etchant. Because the opening width of the third gatetrench 264 is larger than the opening width of the first gate trench260, the patterned photoresist 282 is formed to protect the sacrificialmasking layer 280 in the third gate trench 264 from micro loadingeffect, which causes over etching to the sacrificial masking layer 280in the third gate trench 264, and even damages the first work functionmetal layer 270 under the sacrificial masking layer 280.

Please refer to FIG. 5. Then, another etching back process is performedto remove the first work function metal layer 270 and the inter layer208 not covered by the sacrificial masking layer 280 with proper etchantsuch as ammonium peroxide mixture (APM). In other words, the etchingback process removes the first work function metal layer 270 and theinter layer 208 exposed on the substrate 200 and in the first gatetrench 260 to not filling the first trench 260. The etching back processsimultaneously removes the patterned hard mask 250 on the secondtransistor 212. More important, the etching back process simultaneouslyremoves the overhang 272 formed at the opening of the first gate trench260. Thus the opening width of the first gate trench previously reducedby the overhang 272 is widened to an original opening width. After theetching back process, an U-shaped work function metal layer 274 that iscovered and protected by the sacrificial masking layer 280 is formed inthe first gate trench 260, and the dummy gate 206 of the secondtransistor 212 is exposed.

Please refer to FIG. 6. Then, a proper etchant, such as etchant includesO₂, H₂, and N, is used to remove the sacrificial masking layer 280. Anoxygen concentration of the abovementioned etchant is lower than 10%,thus the first work function metal layer 270 is prevented from oxidationand the semiconductor device is prevented from deterioration duringremoving the sacrificial masking layer 280. In addition, differentetchants can be used to remove the sacrificial masking layer 280depending on the materials used to form the sacrificial masking layer280. For example, when the sacrificial masking layer 280 includesSi-rich material, tetramethylammonium hydroxide (TMAH) solution withconcentration lower than 2.5% is used. It is noteworthy that the etchingback process used to etch back the sacrificial masking layer 280, theetching back process used to remove the overhang 272, the patterned hardmask 250 and the portion of the first work function metal layer 270, andthe removal of the sacrificial masking layer 280 can be in-situperformed. After removing the sacrificial masking layer 280, anotherproper etching process is performed to remove the dummy gate 206 of thesecond transistor 212 to form a second gate trench 262 in the secondtransistor 212 as shown in FIG. 6. It is noteworthy that an openingwidth of the second gate trench 262 is the same with the opening widthof the first gate trench 260. After the etching process used to form thesecond gate trench 262, the gate dielectric layer 204 is exposed in abottom of the second gate trench 262. As mentioned above, when thegate-first process is integrated into the preferred embodiment, the gatedielectric layer 204 includes a high-K gate dielectric layer; when thegate-last process is integrated into the preferred embodiment, the gatedielectric layer can be a conventional SiO layer, and it is removedafter forming the second gate trench 262. Subsequently, a high-K gatedielectric layer 204 having an U shape in the second gate trench 262 isformed. The high-K gate dielectric layer can be chosen from the materialmentioned afore, therefore those details are omitted for simplicity.

Please refer to FIG. 7. In addition, after forming the second gatetrench 262 or after forming the high-K gate dielectric layer, an interlayer (not shown) is formed in the second gate trench 262 if required.The inter layer can be chosen from the material mentioned afore,therefore those details are omitted for simplicity. After forming theinter layer, a second work function metal layer 276 is formed in thefirst gate trench 260, the second gate trench 262, and the third gatetrench 264. It is noteworthy that because the overhang 272 at theopening of the first gate trench 260 is removed, the second workfunction metal layer 276 is easily formed in the gate trenches260/262/264. Furthermore, since the U-shaped work function metal 274 isformed in the first gate trench 260, the second work function metallayer 276 is formed along this peculiar profile and obtains an invertedΩ shape or an inverted bell shape. The inverted Ω-shaped second workfunction metal layer 276 serves as work function metal for n-typetransistor and includes titanium aluminide (TiAl), zirconium aluminide(ZrAl), tungsten aluminide (WAl), tantalum aluminide (TaAl), or hafniumaluminide (HfAl). However, those skilled in the art would easily realizethat the second work function metal layer 276 is not limited to theabovementioned metals, it can include materials having a work functionbetween about 3.9 eV and about 4.3 eV. Furthermore, the second workfunction metal layer 276 can be a single-layered or multi-layeredstructure.

Please still refer to FIG. 7 and FIG. 8. After forming the second workfunction metal layer 276, a filling metal layer 278 filling the firstgate trench 260, the second gate trench 262 and the third gate trench264 is formed on the substrate 200. The filling metal layer 278 is asingle-layered or multi-layered metal layer having superior gap-fillingcharacteristic. The filling metal layer 278 is selected from the groupconsisting of aluminum (Al), titanium (Ti), tantalum (Ta), tungsten (W),niobium (Nb), molybdenum (Mo), copper (Cu), titanium nitride (TiN),titanium carbide (TiC), tantalum nitride (TaN), Ti/W, or Ti/TiN. Asshown in FIG. 8, after forming the filling metal layer 278, aplanarization process is performed to remove the unnecessary fillingmetal layer 278, second work function metal layer 276, first workfunction metal layer 270, and inter layer 208 on the ILD layer 242.Accordingly, a substantially even surface is formed and a semiconductordevice having metal gate is obtained. It is observed that the surface ofthe ILD layer 242 and the top of the filling metal layer 278 areco-planar after planarization process. In addition, since theplanarization process is well-known to those skilled in the art, thedetails are omitted herein in the interest of brevity.

In the first preferred embodiment, the U-shaped work function metallayer 274 is used to provide work function required for p-type metalgate. Therefore, the second work function metal layer 276 and thefilling metal layer 278 serves as a multi-layered filling structure forthe first transistor 210. It is noteworthy that due to the peculiarprofile of the U-shaped work function metal layer 274, the upper openingof the first gate trench 260 is remained imperviously even after formingthe U-shaped work function metal layer 274, and an aspect ratio of thefirst gate trench 260 is consequently reduced. Accordingly, the secondwork function metal layer 276 and the filling metal layer 278 are ableto fill the first gate trench 260 successfully without any seam left,and the reliability of the first transistor 210 is improved. Moreimportant, since the etching back process used to etch back the firstwork function metal layer 270 simultaneously removes the patterned hardmask 250 covering the second transistor 212 according to the preferredembodiment, it economizes steps of forming another the patternedphotoresist for protecting the first transistor 210 when removing thepatterned hard mask 250 in prior art. Consequently, the preferredembodiment economizes process steps, costs, and effectively preventsproblem such as photoresist residues.

Furthermore, It is well-known that there are devices of different linewidths, which from smaller than 30 nm to larger than 5 μm, formed on asingle wafer, the patterned photoresist 282 is formed on the sacrificialmasking layer 280 around devices having line width larger than 0.15 μmfor preventing those devices from over etching due to micro loadingeffect as shown in FIG. 3 and FIG. 4 according to the preferredembodiment. Additionally, it is not limited to perform the etching backprocess directly after forming the sacrificial masking layer 280 withoutforming the patterned photoresist 282 in the case that there is nodevice having line width larger than 0.15 μm in the preferredembodiment.

Please refer to FIGS. 9-12, which are schematic drawings illustrating amethod of manufacturing a semiconductor device having metal gateprovided by a second preferred embodiment of the present invention. Itis noteworthy that in the second preferred embodiment, material choiceof the elements and steps for forming the elements that are the samewith the first preferred embodiment are omitted for the sake ofsimplicity, and the same elements in both the first and second preferredembodiments are designated by the same numerals. Furthermore, only thefirst transistor 210 and the second transistor 212 are shown in FIG. 9for illustrating circumstance when the devices on the wafer are allhaving line widths smaller than 0.15 μm. However, those skilled in theart would easily realize the steps in the case that there are deviceshaving line widths larger than 0.15 μm, such as the third transistor214, according to the first preferred embodiment.

Please refer to FIG. 9. Different from the first preferred embodiment,after forming the first work function metal layer 270 in the first gatetrench 260, the second preferred embodiment further provides apolysilicon layer 280 a and a layer 280 b that is formed by spin-oncoating on the substrate 200 sequentially. The layer 280 b includes aBARC layer, a Si-rich layer with SHB lower than 43%, a SOG layer, a SLAMlayer, or an oxide-rich layer such as DUO™ (manufacturing by HoneywellElectronic Materials), but not limited to this. As mentioned above, thefirst work function metal layer 270 can be a single-layered ormulti-layered structure and includes materials having a work functionbetween about 4.8 eV and about 5.2 eV. As shown in FIG. 9, an overhang272 reducing the opening width of the first gate trench 260 is alwaysformed at the opening of the first gate trench 260 when forming thefirst work function metal layer 270. As mentioned above, an inter layer(not shown) can be formed before forming the first work function metallayer 270 if required. The polysilicon layer 280 a and the layer 280 brespectively serving as the first masking layer and the second maskinglayer construct a multi-layered sacrificial masking layer 280. In otherwords, the sacrificial masking layer 280 provided by the preferredembodiment is a multi-layered structure.

It is noteworthy that in consideration of impact to the first workfunction metal layer 270 from the high temperature for forming thepolysilicon layer 280 a, it is preferable to form the polysilicon layer280 a by low-temperature process. For example, the polysilicon layer 280a can be formed by a physical vapor deposition (PVD). And a thickness ofthe polysilicon layer 280 a is not larger than 150 angstroms (Å). Thepolysilicon layer 280 a is formed to protect the first work functionmetal layer 270 from oxidation in the Q-time that is a period since awafer has been waited to be processed such as the period between formingthe first work function metal layer 270 and the layer 280 b.Furthermore, when rework for the layer 280 b is required due to defectsin the spin-on coating process or the patterning process, thepolysilicon layer 280 a also protects the first work function metallayer 270 when removing the defective layer 280 b.

Please refer to FIG. 10. Next, an etching back process is performed toremove a portion of the sacrificial masking layer 280 in the first gatetrench 260 and on the substrate 200 with proper etchant such as CO, O₂plasma, or preferably CO and HBr. It is observed that when the O₂ plasmaundesirably touches the first work function metal layer 270 duringetching back the sacrificial masking layer 280, oxidation is happened tothe first work function metal layer 270 and performance drift isresulted. However, since the polysilicon layer 280 a renders protectionto the first work function metal layer 270 in the preferred embodiment,the O₂ plasma is obstructed from the first work function metal layer270. After the etching back process, a surface of the sacrificialmasking layer 280 is lower than the opening of the first gate trench 260that is lower than the surface of the ILD layer 242. Accordingly, aportion of the first work function metal layer 270 in the first gatetrench 260 and on the substrate 200 is exposed.

Please still refer to FIG. 10. Then, another etching back process isperformed to remove the exposed first work function metal layer 270 withproper etchant. In other words, the etching back process is performed toremove the first work function metal layer 270 exposed in the first gatetrench 260 and on the substrate 200; the etching back process alsoremoves the patterned hard mask 250 on the second transistor 212. Moreimportant, the etching back process simultaneously removes the overhang272 of the first work function metal layer 270 formed at the opening ofthe first gate trench 260. Thus the opening width of the first gatetrench 260 previously reduced by the overhang 272 is widened to anoriginal opening width. After the etching back process, an U-shaped workfunction metal layer 274 that is covered and protected by thesacrificial masking layer 280 is formed in the first gate trench 260,and the dummy gate 206 of the second transistor 212 is exposed.

Additionally, in accordance with a modification to the preferredembodiment, after forming the first work function metal layer 270 on thesubstrate 200, a portion of the first work function metal layer 270formed on the second transistor 212 is particularly removed.Furthermore, the patterned hard mask 250 can be removed subsequentlyafter removing the first work function metal layer 270 on the secondtransistor 212. Then, the multi-layered sacrificial masking layer 280 isformed on the substrate 200 and followed by performing the etch backprocess, thus the surface of the sacrificial masking layer 280 is lowerthan the opening of the first gate trench 260. As mentioned above, thenanother etching back process is performed to remove the exposed firstwork function metal layer 270 to form the U-shaped work function metallayer 274 in the first gate trench 260 as shown in FIG. 10,

Please refer to FIG. 11. Next, a proper etchant is used to remove thelayer 280 b of the sacrificial masking layer 280. For example, CO or O2plasma can be used. Since the polysilicon layer 208 a protects the firstwork function metal layer 270 from the O2 plasma, oxidation of the firstwork function metal layer 270 is further prevented. As mentioned above,the etching back process used to etch back the sacrificial masking layer280, the etching back process used to remove the overhang 272, thepatterned hard mask 250 and the portion of the first work function metallayer 270, and the removal of the layer 280 b of the sacrificial maskinglayer 280 can be in-situ performed.

Please refer to FIG. 12. After removing the layer 280 b of thesacrificial masking layer 280, another etching process is performed toremove the dummy gate 206 of the second transistor 212 to form a secondgate trench 262 in the second transistor 212 as shown in FIG. 12. Sincethe dummy gate 206 includes polysilicon, the removal of the dummy gate206 simultaneously removes the polysilicon layer 280 a from the firstgate trench 260. As mentioned above, an opening width of the second gatetrench 262 is the same with the opening width of the first gate trench260. After the etching process used to form the second gate trench 262,the gate dielectric layer 204 is exposed in a bottom of the second gatetrench 262. Subsequently, steps of forming a high-K dielectric layer,selectively forming an inter layer, forming a second work function metallayer, forming a filling metal layer, and a planarization process areperformed as mentioned above, and thus omitted for simplicity.

According to the method of manufacturing a semiconductor device havingmetal gate provided by the second preferred embodiment, the sacrificialmasking layer 280 including the polysilicon layer 280 a is provided, andthe polysilicon layer 280 a protects the first work function metal layer270 in the Q-time or rework processes. Furthermore, the polysiliconlayer 280 a protects the first work function metal layer 270 fromoxidation in the etching back processes, and thus the etching backprocess for etching the sacrificial masking layer 280 is improved.

Please refer to FIGS. 13-17, which are schematic drawings illustrating amethod of manufacturing a semiconductor device having metal gateprovided by a third preferred embodiment of the present invention. It isnoteworthy that in the third preferred embodiment, material choice ofthe elements and steps for forming the elements that are the same withthe first preferred embodiment are omitted for the sake of simplicity.Furthermore, though FIGS. 13-17 depict only the circumstance when thedevices on the wafer are all having line widths smaller than 0.15 μm,those skilled in the art would easily realize the steps in the case thatthere are devices having line widths larger than 0.15 μm according tothe first preferred embodiment.

As shown in FIG. 13, a substrate 300 is provided with a plurality of STI302 for providing electrical isolation. A first transistor 310 and asecond transistor 312 are formed on the substrate 300. The firsttransistor 310 includes a first conductivity type and the secondtransistor 312 includes a second conductivity type. The firstconductivity type and the second conductivity type are complementary.The first transistor 210 and the second transistor 212 having thecomplementary conductivity types are electrically isolated from eachother by the STI 302. In the preferred embodiment, the firstconductivity type is the p-type and the second conductivity type is then-type. However, those skilled in the art would easily realize that itis not limited to have the first conductivity type being the n-type andthe second conductivity type is the p-type.

Please refer to FIG. 13. The first transistor 310 and the secondtransistor 312 respectively include a gate dielectric layer 304 and adummy gate (not shown) such as a polysilicon layer. The gate dielectriclayer 304 can be a conventional SiO layer or a high-K gate dielectriclayer. The first transistor 310 and the second transistor 312respectively include a first LDD 320 and a second LDD 322, a spacer 326,a first source/drain 330 and a second source/drain 332, and salicides336 formed on the first source/drain 330 and the second source/drain332. After forming the first transistor 310 and the second transistor312, a CESL 340 and an ILD layer 342 are sequentially formed on thesubstrate 300. Additionally, SEG method can be utilized to form thefirst source/drain 330 and the second source/drain 332 in the preferredembodiment. Since the steps and materials choices for the abovementionedelements are well known to those skilled in the art, those details areomitted herein in the interest of brevity.

Please still refer to FIG. 13. After forming the CESL 340 and the ILDlayer 342, a planarization process is performed to remove a portion ofthe CESL 340 and the ILD layer 342 to expose the dummy gates of thefirst transistor 310 and the second transistor 312. Then, a properetching process is performed to remove the dummy gates of the firsttransistor 310 and the second transistor 312 to forma first gate trench360 in the first transistor 310 and a second gate trench 362 in thesecond transistor 312, respectively. After the etching process, the gatedielectric layer 304 is exposed in the bottom of the first gate trench360 and the second gate trench 362. As mentioned above, the high-K firstprocess can be integrated into the preferred embodiment, and the gatedielectric layer 304 includes a high-K gate dielectric layer. The high-Kmaterials used to form the gate dielectric layer 304 is the same withthose disclosed in the first preferred embodiment, and therefore omittedfor simplicity. Additionally, when the high-K last process is integratedinto the prefer embodiment, and the gate dielectric layer 304 firstincludes a conventional SiO layer. In the high-K last process, the gatedielectric layer 304 exposed in the bottom of the first gate trench 360and the second gate trench 362 are removed and followed by forming ahigh-K gate dielectric layer (not shown).

Please still refer to FIG. 13. Then, a first work function metal layer370 is formed on the substrate 300. As mentioned above, an inter layer308 is selectively formed in the first gate trench 360 and the secondgate trench 362 if required. The inter layer 308 includes a barrierlayer, a strained stress layer, a tuning metal layer, or the combinationthereof, but not limited to this. After forming the first work functionmetal layer 370, a patterning process is performed to remove the firstwork function metal layer 370 from the second gate trench 362.Accordingly, the first work function metal layer 370 remains in thefirst gate trench 360. It is noteworthy that an overhang as depicted inCircle 372 is always formed at the openings of the first gate trench 360when forming the first work function metal layer 370. It is conspicuousthe opening width of the first gate trench 360 is smaller, therefore theoverhang 372 renders more serious impact to the opening width of thefirst gate trench 360. As shown in FIG. 13, the overhang 372 of thefirst work function metal layer 370 reduces the opening width of thefirst gate trench 360. The first work function metal layer 370 serves aswork function metal for p-type transistor and includes materials havinga work function between about 4.8 eV and about 5.2 eV as disclosed inthe first preferred embodiment. Additionally, the first work functionmetal layer 370 can be a single-layered or multi-layered structure. Thefirst work function metal layer 270 can be a single-layered ormulti-layered structure and includes materials having a work functionbetween about 4.8 eV and about 5.2 eV.

Please refer to FIG. 14. After forming the first work function metallayer 370, a sacrificial masking layer 380 is formed on the substrate300. The sacrificial masking layer 380 is a layer have superiorgap-filling characteristic such as a BARC layer, a polysilicon layer, aSi-rich layer with SHB lower than 43%, a SOG layer, a SLAM layer, or anoxide-rich layer such as DUO™ (manufacturing by Honeywell ElectronicMaterials), but not limited to this. As mentioned above, though thesacrificial masking layer 380 is a single-layered structure as shown inFIG. 14, the sacrificial masking layer 380 can be a multi-layeredstructure. As shown in FIG. 14, the sacrificial masking layer 380 isalso formed in the first gate trench 360 and the second gate trench 362.After forming the sacrificial masking layer 380, a patterned photoresist382 is formed on the substrate 300. The patterned photoresist 382exposes the first transistor 310, particularly exposes the sacrificialmasking layer 380 in the first gate trench 360.

Please refer to FIG. 15. Next, an etching back process is performed toremove the exposed sacrificial masking layer 380 to not filling thefirst gate trench 360 with a proper etchant. After the etching backprocess, a surface of the sacrificial masking layer 380 is lower thanthe opening of the first gate trench 360, that is, lower than a surfaceof the ILD layer 342. Thus, a portion of the first work function metallayer 370 on the substrate 300 and in the first gate trench 360 isexposed. During the etching back process, the sacrificial masking layer380 in the second gate trench 362 is protected by the patternedphotoresist 382, therefore it remains impervious to the etchant. Inother words, the sacrificial masking layer 380 still renders protectionto the gate dielectric layer 304 in the second gate trench 362.

Please refer to FIG. 16. Then, another etching back process is performedto remove the first work function metal layer 370 and the inter layer308 not covered by the sacrificial masking layer 380 with properetchant. More important, the etching back process simultaneously removesthe overhang 372 of the first work function metal layer 370 formed atthe opening of the first gate trench 360. Thus the opening width of thefirst gate trench 360 previously reduced by the overhang 372 is widenedto an original opening width. After the etching back process, anU-shaped work function metal layer 374 that is covered and protected bythe sacrificial masking layer 380 is formed in the first gate trench360.

Please refer to FIG. 17. Next, a proper etchant, such as etchantincludes O₂, H₂, and N, is used to remove the patterned photoresist 382and the sacrificial masking layer 380. It is noteworthy that the etchingback process used to etch back the sacrificial masking layer 380, theetching back process used to remove the overhang 372 and the portion ofthe first work function metal layer 370, and the removal of thesacrificial masking layer 380 can be in-situ performed. After removingthe patterned photoresist 382 and the sacrificial masking layer 380, theU-shaped work function metal layer 374 is exposed in the bottom of thefirst gate trench 360 and the gate dielectric layer 304 is exposed inthe bottom of the second gate trench 362. Then steps of forming a high-Kgate dielectric layer (if the high-K last process is integrated),selectively forming an inter layer, forming a second work function metallayer, forming a filling metal layer and planarization process aresequentially performed as mentioned in the first preferred embodimentand thus the details are omitted for simplicity.

In the preferred embodiment, the upper opening of the first gate trench360 is remained imperviously even after forming the U-shaped metal layer374 due to the peculiar profile of the U-shaped work function metallayer 374. Accordingly an aspect ratio of the first gate trench 360 isreduced, and the second work function metal layer and the filling metallayer are able to fill the first gate trench 360 successfully withoutany seam left, and the reliability of the first transistor 310 isimproved.

Furthermore, It is well-known that there are devices of different linewidths, which from smaller than 30 nm to larger than 5 μm, formed on asingle wafer, the patterned photoresist 382 therefore can be formed onthe sacrificial masking layer 380 around devices having line widthlarger than 0.15 μm for preventing those devices from over etching dueto micro loading effect and formed on around devices having conductivitytype opposite to that of the first transistor 310 for protecting thosedevices from etching in the preferred embodiment. Accordingly, thoughthere are lots of transistor devices of different conductivity types andof different line widths, the U-shaped work function metal layer 374 isformed in the desired gate trench without impacting the abovementionedareas according to the preferred embodiment.

Please refer to FIG. 18, which is a drawing illustrating a modificationto the third preferred embodiment. It is noteworthy that the sacrificialmasking layer 380 can be a single-layered structure as shown in FIGS.14-16. The sacrificial masking layer 380 also can be a multi-layeredstructure as shown in FIG. 18. That is, after forming the first workfunction metal layer 370 in the first gate trench 360, a polysiliconlayer 380 a is formed on the substrate 300 and followed by forming alayer 380 b by spin-on coating according to the modification. The layer380 b includes a BARC layer, a Si-rich layer with SHB lower than 43%, aSOG layer, a SLAM layer, or an oxide-rich layer such as DUO™(manufacturing by Honeywell Electronic Materials), but not limited tothis. The polysilicon layer 380 a and the layer 380 b respectivelyserving as the first masking layer and the second masking layerconstruct a multi-layered sacrificial masking layer 380.

As mentioned above, it is noteworthy that in consideration of impact tothe first work function metal layer 370 from the high temperature forforming the polysilicon layer 380 a, it is preferable to form thepolysilicon layer 380 a by low-temperature process such as the PVD. Athickness of the polysilicon layer 380 a is not larger than 150 Å. Thepolysilicon layer 380 a is formed to protect the first work functionmetal layer 370 from oxidation in the Q-time that is a period since awafer has been waited to be processed such as the period between formingthe first work function metal layer 370 and the layer 380 b.Furthermore, when rework for the layer 380 b is required due to defectsin the spin-on coating process or the patterning process, thepolysilicon layer 380 a also protects the first work function metallayer 370 when removing the defective layer 308 b.

According to the modification, the sacrificial masking layer 380including the polysilicon layer 380 a is provided, and polysilicon layer380 a protects the first work function metal layer 370 in the Q-time orrework processes. Furthermore, the polysilicon layer 380 a protects thefirst work function metal layer 370 in the etching back processes, andthus the etching back process for etching the sacrificial masking layer380 is improved.

According to the method of manufacturing a semiconductor device havingmetal gate provided by the present invention, the sacrificial maskinglayer not filling the first gate trench is formed to protect a portionof the first work function metal layer in the first gate trench.Therefore the unnecessary first work function metal layer on thesubstrate and the overhang at the opening of the first gate trench areremoved. Consequently, layers such as the second work function metallayer and the filling metal layer are formed successfully formed in thefirst gate trench without any seam. Therefore the semiconductor devicehaving metal gate provided by the present invention has the advantage ofimproved reliability.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A method of manufacturing a semiconductor devicehaving metal gate comprising: providing a substrate having a firsttransistor and a second transistor formed thereon, the first transistorhaving a first gate trench and a first conductivity type, the secondtransistor having a second conductivity type, and the first conductivitytype and the second conductivity type being complementary; forming afirst work function metal layer only in the first gate trench; forming asacrificial masking layer in the first gate trench; removing a portionof the sacrificial masking layer to expose a portion of the first workfunction metal layer; removing the exposed first work function metallayer to form a U-shaped work function metal layer, wherein topmostportions of the U-shaped work function metal layer are lower than anopening of the first gate trench; and removing the sacrificial maskinglayer.
 2. The method of manufacturing a semiconductor device havingmetal gate according to claim 1, wherein the sacrificial masking layeris a multi-layer, and the multi-layer comprises a first masking layerand a second masking layer.
 3. The method of manufacturing asemiconductor device having metal gate according to claim 2, furthercomprising an etching back process for removing the portion of thesacrificial masking layer to not fill the first gate trench.
 4. Themethod of manufacturing a semiconductor device having metal gateaccording to claim 3, further comprising an etching process performed toremove the first masking layer of the sacrificial masking layer and leftthe second masking layer.
 5. The method of manufacturing a semiconductordevice having metal gate according to claim 1, further comprising anetching back process for removing the portion of the sacrificial maskinglayer to not fill the first gate trench.
 6. The method of manufacturinga semiconductor device having metal gate according to claim 1, whereinthe second transistor further comprises a second gate trench formedtherein, and an opening width of the second gate trench is the same withan opening width of the first gate trench.
 7. The method ofmanufacturing a semiconductor device having metal gate according toclaim 6, wherein the second gate trench and the first gate trench areformed simultaneously, and the second gate trench is filled with thesacrificial masking layer.
 8. The method of manufacturing asemiconductor device having metal gate according to claim 7, furthercomprising forming a first patterned photoresist exposing thesacrificial masking layer in the first gate trench on the sacrificialmasking layer before removing the portion of the sacrificial maskinglayer.
 9. The method of manufacturing a semiconductor device havingmetal gate according to claim 6, further comprising: forming a patternedhard mask on the substrate for covering and protecting the secondtransistor during forming the first gate trench; removing the exposedfirst work function metal layer and the patterned hard masksimultaneously; and forming the second gate trench in the secondtransistor.
 10. The method of manufacturing a semiconductor devicehaving metal gate according to claim 9, wherein the first work functionmetal layer further comprises an overhang, and the overhang issimultaneously removed with removing the exposed first work functionmetal layer and the patterned hard mask.
 11. The method of manufacturinga semiconductor device having metal gate according to claim 6, furthercomprising sequentially forming a second work function metal layer and afilling metal layer in the first gate trench and the second gate trench.12. The method of manufacturing a semiconductor device having metal gateaccording to claim 11, wherein an upper area of the second work functionmetal layer in the first gate trench is wider than a lower area of thesecond work function metal layer.
 13. The method of manufacturing asemiconductor device having metal gate according to claim 1, furthercomprises a third transistor formed on the substrate, and a third gatetrench is formed in the third transistor simultaneously with forming thefirst gate trench, wherein an opening width of the third gate trench islarger than an opening width of the first gate trench.
 14. The method ofmanufacturing a semiconductor device having metal gate according toclaim 13, further comprises steps performed before removing the portionof the sacrificial masking layer to expose the portion of the first workfunction metal layer: forming the sacrificial masking layer in the thirdgate trench; and forming a second patterned photoresist on thesubstrate, the second patterned photoresist covering the thirdtransistor but exposing the first transistor.
 15. A method ofmanufacturing a semiconductor device having metal gate comprising:providing a substrate having a first transistor and a second transistorformed thereon, the first transistor having a first gate trench formedtherein, the second transistor having a second gate trench formedtherein, and an opening width of the second gate trench is larger thanan opening width of the first gate trench; forming a first work functionmetal layer in the first gate trench; forming a sacrificial maskinglayer in the first gate trench and the second gate trench; forming apatterned photoresist covering the second transistor and exposing thesacrificial masking layer in the first gate trench on the substrate;removing a portion of the sacrificial masking layer to expose a portionof the first work function metal layer; and removing the exposed thefirst work function metal layer to form a U-shaped work function metallayer.
 16. The method of manufacturing a semiconductor device havingmetal gate according to claim 15, wherein the sacrificial masking layeris a multi-layer, and the multi-layer comprises a first masking and asecond masking layer.
 17. The method of manufacturing a semiconductordevice having metal gate according to claim 16, further comprising anetching back process for removing the portion of the sacrificial maskinglayer to not fill the first gate trench.
 18. The method of manufacturinga semiconductor device having metal gate according to claim 17, furthercomprising an etching process performed to remove the first maskinglayer of the sacrificial masking layer and left the second maskinglayer.
 19. The method of manufacturing a semiconductor device havingmetal gate according to claim 15, further comprising an etching backprocess for removing the portion of the sacrificial masking layer. 20.The method of manufacturing a semiconductor device having metal gateaccording to claim 15, further comprising removing the sacrificialmasking layer after forming the U-shaped work function metal layer. 21.The method of manufacturing a semiconductor device having metal gateaccording to claim 15, further comprising a third transistor positionedon the substrate, the first transistor and the second transistorcomprise a first conductivity type, the third transistor comprises asecond conductivity type, and the first conductivity type and the secondconductivity type complementary.
 22. The method of manufacturing asemiconductor device having metal gate according to claim 21, whereinthe third transistor further comprises a third gate trench formedsimultaneously with forming the first gate trench and the second gatetrench.
 23. The method of manufacturing a semiconductor device havingmetal gate according to claim 22, wherein an opening width of the thirdgate trench is the same with the opening width of the first gate trench,and the third gate trench is filled with the sacrificial masking layer.24. The method of manufacturing a semiconductor device having metal gateaccording to claim 23, wherein the patterned photoresist covers thesacrificial masking layer in the third gate trench.
 25. The method ofmanufacturing a semiconductor device having metal gate according toclaim 22, further comprising sequentially forming a second work functionmetal layer and a filling metal layer in the first gate trench, in thesecond gate trench and in the third gate trench.
 26. The method ofmanufacturing a semiconductor device having metal gate according toclaim 25, wherein an upper area of the second work function metal layerin the first gate trench is wider than a lower area of the second workfunction metal layer.
 27. The method of manufacturing a semiconductordevice having metal gate according to claim 15, wherein the first workfunction metal layer is simultaneously formed in the second gate trench.